CN103499825B - Method for rapidly capturing BDS weak signals of high-orbit spacecraft - Google Patents

Abstract

Translated fromChinese

一种高轨航天器BDS弱信号快速捕获方法，通过2ms数据重叠累积，利用NH码具有的自相关性移除NH码相位，完成20ms相干累积配合若干次非相干累积的弱信号捕获，采用基于FFT/IFFT的并行码相位搜索策略，提高捕获速度。本发明能够解决由于BDS信号NH码相位未知，导致无法延长相干累积时间的问题。本发明实现的BDS信号捕获灵敏度高、速度快，可广泛应用于高轨、探月返回等航天任务的BDS导航接收机中，具有广阔的推广应用前景。

A fast acquisition method for BDS weak signals of high-orbit spacecraft, through 2ms data overlapping and accumulation, using the autocorrelation of NH codes to remove the phase of NH codes, and completing 20ms coherent accumulation combined with several non-coherent accumulations for weak signal acquisition. The parallel code phase search strategy of FFT/IFFT improves the acquisition speed. The invention can solve the problem that the coherent accumulation time cannot be extended due to the unknown phase of the NH code of the BDS signal. The BDS signal captured by the invention has high sensitivity and fast speed, can be widely used in BDS navigation receivers for space missions such as high-orbit, lunar exploration and return, and has broad application prospects.

Description

Translated fromChinese

一种高轨航天器BDS弱信号快速捕获方法A fast acquisition method for BDS weak signal of high-orbit spacecraft

技术领域technical field

本发明涉及一种高轨航天器BDS（北斗导航系统）弱信号快速捕获技术，可用于对调制有NH码（Neumann-Hoffman码）等二次编码的卫星导航信号进行弱信号快速捕获，属于卫星应用领域。The invention relates to a high-orbit spacecraft BDS (Beidou Navigation System) weak signal fast capture technology, which can be used for fast weak signal capture of satellite navigation signals modulated with secondary codes such as NH codes (Neumann-Hoffman codes), and belongs to satellite application field.

背景技术Background technique

高轨航天器近年来在陆地和海洋通信、气象探测、教育应用、电视直播、灾难预警等方面都发挥着重要作用，特别是地球静止轨道航天器，以其独特的对地静止特性，成为通信、气象、侦察、授时以及跟踪与数据中继和科学研究等地球卫星的重要轨道资源。我国对高轨航天器需求的数量逐年增加，高轨航天器的自主导航已经成为我国迫切需要发展的航天新技术。In recent years, high-orbit spacecraft have played an important role in land and ocean communications, meteorological detection, educational applications, live TV, disaster warning, etc., especially geostationary orbit spacecraft, with its unique geostationary characteristics, have become communication , Meteorology, reconnaissance, timing, tracking and data relay, and scientific research are important orbital resources for earth satellites. my country's demand for high-orbit spacecraft is increasing year by year, and the autonomous navigation of high-orbit spacecraft has become a new aerospace technology that my country urgently needs to develop.

全球卫星导航系统凭借其全球、全天候、连续和高精度的特点，在国防、国家安全、经济安全和社会生活中发挥着重要的作用。我国正在抓紧实施建设具有全球覆盖能力的BDS(北斗导航系统)，预计到2020年具备基本的运行能力。在高轨航天器上使用导航接收机成为各类工程应用的热点。With its global, all-weather, continuous and high-precision characteristics, the global satellite navigation system plays an important role in national defense, national security, economic security and social life. my country is stepping up the implementation of the BDS (BeiDou Navigation System) with global coverage, and it is expected to have basic operational capabilities by 2020. The use of navigation receivers on high-orbit spacecraft has become a hot spot in various engineering applications.

由于高轨航天器轨道高度高于导航星座，接收机需要接收来自地球对面的导航卫星信号。地球的遮挡以及信号传播距离增加造成接收功率降低等因素，将导致使用常规接收技术存在可见星数减少、导航信号持续时间短、接收信号功率微弱等缺点。Since the altitude of the orbit of the high-orbit spacecraft is higher than that of the navigation constellation, the receiver needs to receive signals from the navigation satellites on the opposite side of the earth. Factors such as the occlusion of the earth and the decrease in received power caused by the increase of signal propagation distance will lead to the disadvantages of reducing the number of visible stars, short duration of navigation signals, and weak received signal power when using conventional receiving technology.

解决接收导航信号功率微弱的基本思路是采用多周期信号能量累积，通过对多个1ms相关值的累积求和（相干累积、非相干累积），带来信噪比提升。但是BDS存在NH码，将在捕获过程中，由于NH码相位未知导致相干累积长度受限的问题；若仅采用非相干累积处理，此时需要处理的数据将比相干累积时的数据更加庞大，同时降低了捕获速度，从而造成高轨接收BDS信号的困难。The basic idea to solve the weak power of the received navigation signal is to use multi-period signal energy accumulation, and through the accumulation and summation of multiple 1ms correlation values (coherent accumulation, non-coherent accumulation), the signal-to-noise ratio is improved. However, there is an NH code in BDS, and during the acquisition process, the coherent accumulation length is limited due to the unknown phase of the NH code; if only non-coherent accumulation processing is used, the data to be processed at this time will be larger than the data in coherent accumulation. At the same time, the acquisition speed is reduced, which makes it difficult to receive BDS signals on the high track.

发明内容Contents of the invention

本发明的技术解决问题是：克服现有技术的不足，提供一种高轨航天器BDS弱信号快速捕获方法，本发明能克服由于NH码相位未知而限制相干累积长度导致无法高效提升累积处理增益的问题，可用于设计具有较高捕获灵敏度水平的BDS导航接收机，实用性强。The technical solution of the present invention is to overcome the deficiencies of the prior art and provide a fast acquisition method for high-orbit spacecraft BDS weak signals. The present invention can overcome the limitation of the coherent accumulation length due to the unknown NH code phase, which leads to the inability to efficiently improve the accumulation processing gain. It can be used to design a BDS navigation receiver with a higher acquisition sensitivity level, and has strong practicability.

本发明的技术解决方案是：Technical solution of the present invention is:

一种高轨航天器BDS弱信号快速捕获方法，包括步骤如下：A high-orbit spacecraft BDS weak signal fast acquisition method, comprising the following steps:

（1）获取本地多普勒频移值下的1ms数据，将其补零至2ms，并对该数据进行FFT变换，取共轭后得到数据1；(1) Obtain the 1ms data under the local Doppler frequency shift value, fill it with zeros to 2ms, and perform FFT transformation on the data, and obtain data 1 after taking the conjugate;

（2）将接收的中频信号进行数字采样后分别进行连续的2ms数据缓存，即第1ms与第2ms进行缓存，第2ms与第3ms进行缓存，依次缓存20组，得到数据2；(2) After the received intermediate frequency signal is digitally sampled, continuous 2ms data buffering is performed respectively, that is, 1st and 2ms are buffered, 2ms and 3rd ms are buffered, and 20 groups are buffered in turn to obtain data 2;

（3）将步骤（2）中得到的数据2中的每组2ms数据分别依次与20比特NH码的一个码片相乘，所述NH码为0,0,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,1,0，得到20组与NH码相乘之后的数据3；(3) Multiply each group of 2ms data in the data 2 obtained in step (2) by one chip of the 20-bit NH code in turn, and the NH code is 0,0,0,0,0,1, 0,0,1,1,0,1,0,1,0,0,1,1,1,0, get 20 sets of data 3 multiplied by NH code;

（4）对步骤（3）得到数据3中的20组2ms数据进行相干累积，得到长度为2ms的相干累积值，并进行FFT操作得到数据4；(4) Perform coherent accumulation on the 20 groups of 2ms data in data 3 obtained in step (3), obtain a coherent accumulation value with a length of 2ms, and perform FFT operation to obtain data 4;

（5）分别将数据4和数据1依次对位进行相乘，得到数据5，对数据5再进行IFFT变换得到数据6；(5) Multiply data 4 and data 1 in sequence to obtain data 5, and perform IFFT transformation on data 5 to obtain data 6;

（6）对数据6进行多次非相干累积，得到1组数据7；(6) Perform multiple non-coherent accumulations on data 6 to obtain a set of data 7;

（7）利用奈曼-皮尔斯准则对数据7进行捕获门限判决，判断是否成功捕获信号，若成功捕获信号进入步骤（9），否则判断20个NH码相位是否搜索完成，若没有搜索完成则进入步骤（8），若搜索完成更改本地多普勒频移值进入步骤（1）；(7) Use the Neyman-Pierce criterion to judge the capture threshold of data 7 to determine whether the signal is successfully captured. If the signal is successfully captured, enter step (9), otherwise, determine whether the search for the 20 NH code phases is completed. If not, enter Step (8), if the search is completed, change the local Doppler frequency shift value and enter step (1);

（8）对20比特的NH码循环移位一个码片，进入步骤(2)，重复步骤（2）～(7)；(8) Cyclically shift the 20-bit NH code by one chip, enter step (2), and repeat steps (2) to (7);

（9）捕获结束。(9) CAPTURE END.

本发明与现有技术相比的有益效果是：The beneficial effect of the present invention compared with prior art is:

（1）本发明针对相干累积时NH码相位未知导致无法进行长时间累积问题，采用对2ms数据的重叠累积，消除了该影响，延长相干累积时间至20ms，从而提高BDS信号的捕获灵敏度。(1) The present invention aims at the problem that the phase of the NH code is unknown during coherent accumulation, which leads to the inability to perform long-term accumulation. It adopts the overlapping accumulation of 2ms data to eliminate the impact, and prolongs the coherent accumulation time to 20ms, thereby improving the acquisition sensitivity of BDS signals.

（2）本发明采用了对重叠累积值进行非相干累积的方式，进一步提高处理增益。(2) The present invention adopts the way of non-coherent accumulation of overlapping accumulation values to further improve the processing gain.

（3）本发明采用基于FFT/IFFT并行码相位快速搜索，工程上极大得提高了捕获速度，降低了对20msNH码自相关运算带来的资源损耗。(3) The present invention uses FFT/IFFT-based parallel code phase fast search, which greatly improves the capture speed in engineering and reduces the resource loss caused by the autocorrelation operation of the 20msNH code.

附图说明Description of drawings

图1为本发明方法流程图；Fig. 1 is a flow chart of the method of the present invention;

图2为本发明2ms数据重叠累积的NH码搜索原理示意图；Fig. 2 is the NH code search principle schematic diagram of 2ms data overlapping accumulation of the present invention;

图3本发明为输入信号与NH码相乘示意图；Fig. 3 the present invention is the multiplication schematic diagram of input signal and NH code;

图4本发明为NH码自相关示意图；Fig. 4 the present invention is NH code autocorrelation schematic diagram;

图5本发明为2ms数据重叠累积处理流程示意图。Fig. 5 is a schematic diagram of the processing flow of 2ms data overlap and accumulation in the present invention.

具体实施方式Detailed ways

下面结合附图对本发明的具体实施方式进行进一步的详细描述。Specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

本发明提供的一种高轨BDS弱信号快速捕获方法，可用于设计具有弱信号处理能力BDS导航接收机，本发明通过2ms数据重叠累积来移除NH码相位，完成20ms相干累积配合若干次非相干累积的弱信号捕获过程，并采用基于FFT/IFFT的并行码相位搜索策略，提高捕获速度。The present invention provides a high-rail BDS weak signal fast acquisition method, which can be used to design a BDS navigation receiver with weak signal processing capability. The present invention removes the NH code phase through 2ms data overlap and accumulation, and completes 20ms coherent accumulation with several non- The weak signal acquisition process of coherent accumulation, and the parallel code phase search strategy based on FFT/IFFT are adopted to improve the acquisition speed.

如图1所示，本发明的具体步骤如下：As shown in Figure 1, the concrete steps of the present invention are as follows:

（1）获取本地多普勒频移值下的1ms数据，将其补零至2ms，并对该数据进行FFT变换，取共轭后得到数据1；(1) Obtain the 1ms data under the local Doppler frequency shift value, fill it with zeros to 2ms, and perform FFT transformation on the data, and obtain data 1 after taking the conjugate;

（2）将接收的中频信号进行数字采样后分别进行连续的2ms数据缓存，即第1ms与第2ms进行缓存，第2ms与第3ms进行缓存，依次缓存20组，得到数据2；(2) After the received intermediate frequency signal is digitally sampled, continuous 2ms data buffering is performed respectively, that is, 1st and 2ms are buffered, 2ms and 3rd ms are buffered, and 20 groups are buffered in turn to obtain data 2;

（3）将步骤（2）中得到的数据2中的每组2ms数据分别依次与20比特NH码的一个码片相乘，所述NH码为0,0,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,1,0，得到20组与NH码相乘之后的数据3；(3) Multiply each group of 2ms data in the data 2 obtained in step (2) by one chip of the 20-bit NH code in turn, and the NH code is 0,0,0,0,0,1, 0,0,1,1,0,1,0,1,0,0,1,1,1,0, get 20 sets of data 3 multiplied by NH code;

（4）对步骤（3）得到数据3中的20组2ms数据进行相干累积（例如：第1组2ms数据与第2组2ms进行累积，累积后的结果再与第3组2ms的数据进行累积，直到20组2ms数据相干累积结束），得到长度为2ms的相干累积值，并进行FFT操作得到数据4；(4) Coherently accumulate 20 groups of 2ms data in data 3 obtained in step (3) (for example: the first group of 2ms data is accumulated with the second group of 2ms, and the accumulated result is then accumulated with the third group of 2ms data , until the coherent accumulation of 20 groups of 2ms data ends), the coherent accumulation value with a length of 2ms is obtained, and the FFT operation is performed to obtain data 4;

（5）分别将数据4和数据1依次对位进行相乘，得到数据5，对数据5再进行IFFT变换得到数据6；(5) Multiply data 4 and data 1 in sequence to obtain data 5, and perform IFFT transformation on data 5 to obtain data 6;

（6）对数据6进行多次非相干累积，得到1组数据7；对数据6进行非相干累积的次数与捕获灵敏度有关，要求的捕获灵敏度越高，进行非相干累计的次数越多；(6) Perform multiple non-coherent accumulations on data 6 to obtain a set of data 7; the number of non-coherent accumulations on data 6 is related to the capture sensitivity. The higher the required capture sensitivity, the more times to perform non-coherent accumulations;

（7）利用奈曼-皮尔斯准则对数据7进行捕获门限判决，判断是否成功捕获信号，若成功捕获信号进入步骤（9），否则判断20个NH码相位是否搜索完成，若没有搜索完成则进入步骤（8），若搜索完成更改本地多普勒频移值进入步骤（1）；(7) Use the Neyman-Pierce criterion to judge the capture threshold of data 7 to determine whether the signal is successfully captured. If the signal is successfully captured, enter step (9), otherwise, determine whether the search for the 20 NH code phases is completed. If not, enter Step (8), if the search is completed, change the local Doppler frequency shift value and enter step (1);

（8）对20比特的NH码循环移位一个码片，进入步骤(2)，重复步骤（2）～(7)；(8) Cyclically shift the 20-bit NH code by one chip, enter step (2), and repeat steps (2) to (7);

（9）捕获结束。(9) CAPTURE END.

结合特定工程实施案例，给出技术具体实施方式及仿真验证结果：Combined with specific engineering implementation cases, the specific implementation methods and simulation verification results of the technology are given:

（一）2ms数据重叠累积去除NH码相位设计(1) 2ms data overlap accumulation removal NH code phase design

如图2、3所示，2ms数据重叠累积的NH码搜索原理和流程，对2ms数据的处理流程见图2。As shown in Figures 2 and 3, the NH code search principle and flow for 2ms data overlapping and accumulating, and the processing flow for 2ms data is shown in Figure 2.

假设输入信号与NH码序列的相位差为ξ，此时连续的2ms数据依次与NH码相乘的结果为：D_k=[(1-ξ)·N_k,N_k+1,ξ·N_k+2]×N_k+1Assuming that the phase difference between the input signal and the NH code sequence is ξ, the result of multiplying the continuous 2ms data with the NH code sequence is: D_k =[(1-ξ)·N_k ,N_k+1 ,ξ·N_k+2 ]×N_k+1

将20组D_k数据依次相加：Add 20 sets of D_k data sequentially:

$\begin{array}{c}\mathrm{<span><span>\&Sigma;</span>\&Sigma;</span>}{\mathrm{<span><span>D</span>D.</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>=</span>=</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>\&xi;</span>\&xi;</span>}<span><span>)</span>)</span><span><span>\&times;</span>\&times;</span>\underset{\mathrm{<span><span>k</span>k</span>}<span><span>=</span>=</span>\mathrm{<span><span>1</span>1</span>}}{\overset{\mathrm{<span><span>20</span>20</span>}}{\mathrm{<span><span>\&Sigma;</span>\&Sigma;</span>}}}{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>\&times;</span>\&times;</span>{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}<span><span>+</span>+</span>\mathrm{<span><span>1</span>1</span>}}<span><span>+</span>+</span>\underset{\mathrm{<span><span>k</span>k</span>}<span><span>=</span>=</span>\mathrm{<span><span>1</span>1</span>}}{\overset{\mathrm{<span><span>20</span>20</span>}}{\mathrm{<span><span>\&Sigma;</span>\&Sigma;</span>}}}{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}<span><span>+</span>+</span>\mathrm{<span><span>1</span>1</span>}}<span><span>\&times;</span>\&times;</span>{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}<span><span>+</span>+</span>\mathrm{<span><span>1</span>1</span>}}<span><span>+</span>+</span>\mathrm{<span><span>\&xi;</span>\&xi;</span>}<span><span>\&times;</span>\&times;</span>\underset{\mathrm{<span><span>k</span>k</span>}<span><span>=</span>=</span>\mathrm{<span><span>1</span>1</span>}}{\overset{\mathrm{<span><span>20</span>20</span>}}{\mathrm{<span><span>\&Sigma;</span>\&Sigma;</span>}}}{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}<span><span>+</span>+</span>\mathrm{<span><span>2</span>2</span>}}<span><span>\&times;</span>\&times;</span>{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}<span><span>+</span>+</span>\mathrm{<span><span>1</span>1</span>}}\\ <span><span>=</span>=</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>\&xi;</span>\&xi;</span>}<span><span>)</span>)</span><span><span>\&times;</span>\&times;</span>{\mathrm{<span><span>R</span>R</span>}}_{\mathrm{<span><span>N</span>N</span>}}<span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>)</span>)</span><span><span>+</span>+</span>\mathrm{<span><span>20</span>20</span>}<span><span>\&times;</span>\&times;</span>{\mathrm{<span><span>R</span>R</span>}}_{\mathrm{<span><span>N</span>N</span>}}<span><span>(</span>(</span>\mathrm{<span><span>0</span>0</span>}<span><span>)</span>)</span><span><span>+</span>+</span>\mathrm{<span><span>\&xi;</span>\&xi;</span>}<span><span>\&times;</span>\&times;</span>{\mathrm{<span><span>R</span>R</span>}}_{\mathrm{<span><span>N</span>N</span>}}<span><span>(</span>(</span><span><span>-</span>-</span>\mathrm{<span><span>1</span>1</span>}<span><span>)</span>)</span>\end{array}$

式中R_N()为NH码不同码相位对应的自相关值。如图4所示，为NH码的自相关函数，根据图4可知在码相位1和-1处，NH码的自相关值均为0，而码相位0处的自相关值最大。故由上式运算可知，通过对20组2ms数据的累积，中间的1ms可以完全消除NH码相位的影响，具体示意图见图5。In the formula, R_N () is the autocorrelation value corresponding to different code phases of the NH code. As shown in Figure 4, it is the autocorrelation function of the NH code. According to Figure 4, at the code phase 1 and -1, the autocorrelation value of the NH code is 0, and the autocorrelation value at the code phase 0 is the largest. Therefore, it can be seen from the above formula that through the accumulation of 20 sets of 2ms data, the middle 1ms can completely eliminate the influence of the NH code phase. The specific schematic diagram is shown in Figure 5.

采用该方式，将2ms累积所得的中间1ms数据与本地的1ms数据相关，寻找相关峰值，等效于进行了20次相干累积的增益。In this way, the intermediate 1 ms data accumulated in 2 ms is correlated with the local 1 ms data to find the correlation peak, which is equivalent to the gain of 20 times of coherent accumulation.

本发明说明书中未作详细描述的内容属于本领域技术人员的公知技术。The contents not described in detail in the description of the present invention belong to the well-known technology of those skilled in the art.

Claims (1)

1. a high rail spacecraft BDS weak signal quick capturing method, is characterized in that step is as follows:

(1) obtain the 1ms data under local values of Doppler frequency shift, by its zero padding to 2ms, and FFT conversion is carried out to these data, after getting conjugation, obtain data 1;

(2) carry out continuous print 2ms data buffer storage respectively after the intermediate-freuqncy signal of reception being carried out digital sample, namely 1ms and 2ms carries out buffer memory, and 2ms and 3ms carries out buffer memory, and buffer memory 20 groups, obtains data 2 successively;

(3) the 2ms data of often organizing in the data 2 obtained in step (2) be multiplied with a chip of 20 bit NH codes successively respectively, described NH code is 0,0,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,1,0, obtain 20 groups to be multiplied with NH code after data 3;

(4) coherent accumulation is carried out to 20 groups of 2ms data that step (3) obtains in data 3, obtains the coherent accumulation value that length is 2ms, and carry out FFT operation obtain data 4;

(5) respectively data 4 are multiplied with data 1 successively contraposition, obtain data 5, IFFT conversion is carried out to data 5 again and obtains data 6;

(6) repeatedly non-coherent accumulation is carried out to data 6, obtain 1 group of data 7;

(7) Nai Man-Pierre's Si criterion is utilized to carry out detection threshold judgement to data 7, judge whether successfully lock-on signal, if successful lock-on signal enters step (9), otherwise judge whether 20 NH code phases have been searched for, if do not have search to complete, enter step (8), if searched for the local values of Doppler frequency shift of change to enter step (1);

(8) to NH code ring shift chip of 20 bits, enter step (2), repeat step (2) ~ (7);

(9) end is caught;

In step (6), the number of times of non-coherent accumulation carries out to data 6 relevant with acquisition sensitivity.